ABSTRACT
The demonstration over three decades ago (1) of the conversion of vitamin D3 into 25hydroxyvitamin D3 (25-OH-D3) triggered a dramatic surge of interest in the basic biochemistry and physiology of vitamin D. The resultant elucidation of the metabolism and role of vitamin D in calcium homeostasis (1-5) has led to a change of emphasis from the study of the parent vitamin itself to the study of its metabolites. Older methods of bioassay, colorimetric, and ultraviolet (UV) absorption assay have been replaced by newer techniques based upon chromatography, radioligand procedures, and mass spectrometry (reviewed in 6, 7). Present methods separate and specifically measure a wide variety of metabolites and chemical analogs instead of a heterogeneous “vitamin D” group. The increased sensitivity and specificity offered by modern assays have enabled the measure-ment of picogram quantities of vitamin D metabolites, thereby permitting these techniques to be applied to the analysis of vitamin D and its metabolites in physiological fluids. Chemical synthesis of vitamin D metabolites and analogs for clini-cal trials has led to improvements in the separation and analysis of the vitamin D family of compounds, which has also been beneficial to analytical chemists in the pharmaceutical and food industries.
